Fixing the risks around Wall Street's too-big-to-fail problem tends to run into one stubborn hurdle: Risk is where the biggest opportunities for returns often lie.

The latest proposal to deal with it comes from House Ways and Means Chairman Rep. Dave Camp, who recently advocated a new tax on the assets of America's biggest banks. By penalising scale, this would in theory encourage banks to shrink, thereby making the risks inherent to them less systemic.

But like earlier, similar proposals, this one could have the unintended consequence of encouraging Wall Street to do what comes most naturally to it: take on more risk.

Rep. Camp's proposal shares some similarity with the "financial responsibility fee" called for by President Barack Obama in 2010. This would have required banks with consolidated net assets of more than $50 billion to pay a tax equal to 0.15% of leveraged assets. The latter subtracts Tier 1 capital and federally insured deposits from a bank's taxable assets, thereby rewarding banks that build up this kind of buffer.

Rep. Camp's tax would also focus on size, only more so, by dispensing with leverage as a criterion. It would impose a 0.35% excise tax on financial institutions' total assets in excess of $500 billion.

The differences on treatment of leverage means the two proposals would affect the country's biggest banks to different degrees. The Camp tax, for instance, would be far less costly to Goldman Sachs, Morgan Stanley and Citigroup than the president's. Goldman's insured deposit base is small, about one-fifteenth the size of Bank of America's, while Citigroup has a lot of foreign deposits that wouldn't qualify for exclusion from its taxable assets.

The bigger point, though, is that either tax could encourage banks to take on more risks. Faced with an increased cost in holding a dollar's worth of assets, whichever way the balance sheet gets sliced up, banks would almost certainly seek out higher returns on each of those dollars. And the road to higher returns is nearly always paved with the stones of risk.

Rep. Camp's tax proposal looks set to meet the same fate as President Obama's; That is, it will likely take a permanent seat in legislative limbo. Investors should draw two things from this, though.

First, the seemingly straightforward tool of taxing size to reduce it faces an inherent problem in terms of optimising the banking industry's risk to the wider economy.

Second, though, that problem means the eventual set of rules to deal with too-big-to-fail could take a more creative, or convoluted, form that investors aren't prepared for. And seeing the Republican chairman of one of the House's most powerful committees propose a tax on bank assets is a clear signal that Wall Street remains in the cross hairs.